Conventionally, as a control of a node in the communications system, an operation mode of the node is switched (i.e., transitions) to a sleep mode in which functions of the node is somewhat restricted upon determining a fulfillment of a preset sleep condition, for a power saving of an entire communications system.
According to a disclosure in a patent document, JP 2014-104937 A (patent document 1), in each of the nodes of such a system, a power supply to a microcomputer that controls a driver and/or communications is stopped, and a state of a transmission line is monitored (by a controller) in the sleep mode.
When a signal transmission on the transmission line is detected by the controller, the power supply to the driver and/or the microcomputer is resumed, for the transition to a wake-up mode.
In such a technique of the communications system, when one of the network node outputs a signal to the transmission line in the sleep mode, all nodes transition to the wake-up mode. Therefore, selectively waking-up only the required nodes is not performable by such a technique, and communications involving only limited number of nodes wake up all the nodes in the system, thereby diminishing the power consumption reduction effect of the sleep mode.